Organization and Basis of Presentation - Summary of Financial Securities (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Equity securities:
Gross Unrealized Gain (Loss)	$ 23,772	$ 2,215
Carrying Value	2,500		$ 2,500
Available for sale
Equity and Debt Securities, Amortized Cost	143,014		131,770
Equity and Debt Securities, Gross Unrealized Gain (Loss)	40,126		15,998
Equity and Debt Securities, Marketable Securities	183,140		147,768
Investment funds - debt securities
Equity securities:
Cost	61,885		49,646
Gross Unrealized Gain (Loss)	24		985
Carrying Value	61,909		50,631
Common stock and stock funds
Equity securities:
Cost	80,079		81,074
Gross Unrealized Gain (Loss)	39,734		15,001
Carrying Value	119,813		96,075
Investment-grade unsecured debt
Available for sale
Cost	1,050		1,050
Gross Unrealized Gain (Loss)	368		12
Carrying Value	$ 1,418		$ 1,062

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